1. (Field of the Invention)
The present invention relates to a frame opening and closing mechanism provided with a torsion bar for a clamshell type image forming apparatus, such as an electrostatic photographic copying machine and facsimile machine, and the like. In particular, the present invention relates to a frame opening and closing mechanism provided with a torsion bar which has an upper split frame connected with a lower split frame so as to be opened and closed around a horizontal axis shaft line, a connecting portion for biasing the upper split frame in an opened direction, and an opening regulator for allowing the upper split frame to be opened to a predetermined open angle.
2. (Prior Art)
FIGS. 13 and 14 show a prior art frame opening and closing mechanism which uses a torsion bar. In order to bias the upper split frame in the open direction in the frame opening and closing mechanism, a connection member 32 is connected with both sides of the upper split frame in a back and forth direction (a direction meeting at right angles with the paper surface in FIG. 13) of the upper split frame 31. A frame connection member 34 is connected with a lower split frame 33 and pivots on the connection member 32 through a cylindrical connection 35. Two cranklike torsion bars 36, 36 are each provided with bent ends inserted into the cylindrical connection 35, and a twisted shaft portion s of the torsion bar 36 is twisted so as to connect a biasing reaction force portion t of each torsion bar 36 on the frame connection member 34. Another biasing reaction force portion u is on the connection member 32, giving a biasing force in the open direction to the upper split frame 31, as disclosed, for example, in Japanese Utility Model Laid-Open No. Sho 62-82670, and here shown in FIGS. 13 and 14.
However, since the biasing reaction force portions t, u of the above described torsion bars 36, 36 are bent, disadvantages have occurred, in that they are remarkably difficult to insert into the cylindrical connection 35. It is required, for giving a sufficient biasing force in the opened direction to the split frame 31 under the opening regulating condition of the upper split frame 31, that a revolution regulating member 37 is engaged with an openness regulating member 38, and that the twisted shaft portion s of the torsion bar 36 be greatly twisted in order to be set on both the members 32, 34, thus expending much labor.